The present invention generally relates to lighting systems and related technologies. More particularly, this invention relates to materials and methods suitable for imparting color filtering effects to light sources, nonlimiting examples of which include edge-lit lighting units comprising a lightguide coupled with a light source (for example, one or more light-emitting diodes (LEDs)) at an edge of the lightguide.
LED lamps (bulbs) are capable of providing a variety of advantages over more traditional incandescent and fluorescent lamps, including but not limited to a longer life expectancy, high energy efficiency, and full brightness without requiring time to warm up. As known in the art, LEDs (which as used herein also encompasses organic LEDs, or OLEDs) are solid-state semiconductor devices that convert electrical energy into electromagnetic radiation that includes visible light. An LED typically comprises a chip (die) of a semiconducting material doped with impurities to create a p-n junction. The LED chip is electrically connected to an anode and cathode, all of which are often mounted within a package. LEDs emit visible light that is more directional in a narrower beam as compared to other light sources such as incandescent and fluorescent lamps. As such, LEDs have traditionally been utilized in applications such as automotive, display, safety/emergency, and directed area lighting. However, advances in LED technology have enabled high-efficiency LED-based lighting systems to find wider use in lighting applications that have traditionally employed other types of lighting sources, including omnidirectional lighting applications previously served by incandescent and fluorescent lamps. As a result, LEDs are increasingly being used for area lighting applications in residential, commercial and municipal settings.
FIGS. 1 and 2 schematically represent a portion of an edge-lit light fixture or luminaire 10 that includes a light source 12 (FIG. 2) disposed in a fixture housing 14. The light source 12 is represented in FIG. 2 as comprising an LED device, which can be one of any number of LEDs in an array within the fixture housing 14, with the LEDs typically facing in the same direction and each LED effectively being a discreet point light source. As such, the fixture housing 14 is configured to point the LED devices 12 in a direction to direct the light emanating from the luminaire 10. As a nonlimiting example, the luminaire 10 can be configured to illuminate the shelving and contents of a commercial refrigerated display case. Another type of edge-lit luminaire is referred to as a recessed troffer, which is commonly used for drop ceilings in commercial and retail space. Still other applications for edge-lit luminaires include signage, an example of which is “exit” signs commonly used in commercial and retail space.
For illumination applications of the types noted above, the luminaire 10 is shown as further comprising a lightguide 16 having an edge 18 (FIG. 2) disposed in proximity to the array of LED devices 12. As known in the art, the lightguide 16 is an optic component commonly employed in edge-lit technologies. Lightguides are formed to have a surface microstructure adapted to achieve total internal reflection (TIR) to direct light from a light source to a desired application space. The lightguide 16 may be visible from multiple directions, and is typically desired to have a uniform luminance while illuminating a specified area with a desired light level. Depending on the particular application, materials commonly employed to produce lightguides include optical grade transparent materials such as acrylics, though various other materials may be used, for example, polyamides (nylon), polycarbonate (PC), polystyrene (PS), and polypropylene (PP).
Because LED devices emit visible light in narrow bands of wavelengths, for example, green, blue, red, etc., combinations of different LED devices are often combined in LED-based lamps to produce various light colors, including white light. The LED devices are often mounted on a carrier, and may be encapsulated on the carrier, for example, with a protective cover, often formed of an index-matching material to enhance the efficiency of visible light extraction from the LED devices. As a nonlimiting example, FIG. 2 represents the LED device 12 mounted on a carrier 20 and enclosed by a dome 22 that serves as an optically transparent or translucent envelope enclosing an LED chip (not shown) on the carrier 20. A phosphor may also be used to emit light of color other than what is generated by an LED. For this purpose, the inner surface of the dome 22 may be provided with a coating that contains a phosphor composition, in which case electromagnetic radiation (for example, blue visible light, ultraviolet (UV) radiation, or near-visible ultraviolet (NUV) radiation) emitted by the LED chip can be absorbed by the phosphor composition, resulting in excitation of the phosphor composition to produce visible light that is emitted through the dome 22. As an alternative, the LED chip may be encapsulated on the carrier 20 with a coating, and such a coating may optionally contain a phosphor composition for embodiments in which LED-phosphor integration with LED epitaxial (epi) wafer or die fabrication is desired.
Though the use of combinations of different LED devices and/or phosphors can be utilized to promote the ability of luminaires equipped with lightguides to produce desired lighting effects, certain desirable lighting effects can be somewhat challenging to achieve with such approaches. A notable example is the lighting effect achieved with the REVEAL line of incandescent bulbs commercially available from GE Lighting, which are produced to have an outer jacket formed of a glass doped with neodymium oxide (neodymia, Nd2O3) to filter certain wavelengths of light. Lighting effects similar to that achieved with the REVEAL line of incandescent bulbs would also be desirable for luminaires equipped with lightguides.